In the treatment or processing of biological liquid such as blood; equipment has been provided whereby red blood cells, white cells, plasma, and platelet components are separated from whole blood in a centrifuge. In the course of processing blood within the centrifuge, portions of the separated blood components are either retained for storage or transferred to another patient or are returned to the donor. The blood processing may take place intervivos as is shown in U.S. Pat. No. 4,146,172 dated Mar. 27, 1979 entitled Centrifugal Liquid Processing System to Cullis et al.
In other centrifuge blood processing systems the process is not completely intervivos and the centrifuge may be stopped as the blood is processed into its constituent component elements and then some or all of the separated elements are stored or returned to the donor as the case may be. Such a system is described in U.S. patent application Ser. No. 005,126 filed Jan. 22, 1979, now U.S. Pat. No. 4,303,193, entitled Apparatus for Separating Blood into Components Thereof to Allen Latham, Jr.
U.S. Pat. No. 3,679,128 entitled Centrifuge issued July 25, 1972 to Unger et al also shows a centrifuge for processing blood in which an electromagnetic valve operates to control the flow of processed blood from one container to another container during the centrifuge process--that is to say, while the centrifuge rotor is spinning.
In each of the above-described processes it is desirable to provide a simple and reliable mechanism to control the timing of the separation procedures. Preferably such a timing mechanism should operate in a manner directly proportional to the magnitude of the centrifugal force field since it is this quantity that directly influences the blood separation process.
Present controlling means usually operate on the basis of an electronic or electromagnetic switch which is coupled into the centrifuge through slip rings or other means and is remotely operated based on some predetermined time or sensor setting. For example, see the valve 22 in U.S. Pat. No. 3,679,128 or the hydraulically actuated clamp 142 in patent application Ser. No. 005,126 previously referenced.
Such prior art systems suffer from the same drawback; variations in the rotational speed of the rotor are not automatically compensated for and must be compensated for by some other means. In addition, prior art systems require means to transmit a control signal to the rotor through some form of slip seal. These seals are expensive and tend to have short life expectancies in application.